A trocar generally comprises two major components, a trocar tube and an obturator. The trocar tube is inserted through the skin to access a body cavity. It is through the tube in which laparoscopic or arthroscopic surgery is performed. In order to penetrate the skin, the distal end of the trocar tube is placed against the body and an obturator is inserted through the tube. By pressing against the proximal end of the obturator, the point of the obturator is forced through the skin until it enters the body cavity. At this time, the trocar tube is inserted through the perforation made by the obturator. The obturator is withdrawn, leaving the trocar tube as an accessway to the body cavity.
It has been found that some resistive force is required to cause the obturator point to penetrate the skin and underlying tissue. When the point finally breaks through this tissue, resistance to penetration is suddenly removed, and the obturator point can penetrate to reach within the body cavity. To avert danger to the patient, trocars have been developed which carry a spring-loaded tubular shield within the trocar tube and surrounding the obturator. The distal end of the shield presses against the skin as the obturator point penetrates the body, until the obturator has formed a perforation with a diameter sufficient to allow the shield to pass through. At that time the resistance of the tissue to the spring-loaded shield is removed, and the shield springs forward to extend into the body cavity, surrounding the point of the obturator. Thus, the shield thus protects the internal body organs from inadvertent contact with the point of the obturator. A trocar including such a safety shield is described in U.S. Pat. No. 4,535,773, for example.
Yet, in some procedures it may be desirable to have the trocar nonshielded throughout the time when the trocar is placed within the trocar tube cannula. In this way, the user is able to slightly withdraw the trocar from the pierced tissue, and then continue piercing. This prevents what is commonly referred to as "tenting" of pneuoperitoneum. In this fashion, tenting can be reduced, and usage of trocars can adequately provide for access to the body. Also, if the trocar can be seen entering the body, for instance through an inserted scope device, any danger to the patient is avoided by closely following the path of the oburator tip with the scope.
With current shielded trocars, it is necessary to remove the cannula handle from the obturator handle to "reload" the shield on the trocar. In this fashion, therefore, it is necessary to perform an extra step while the obturator tip is inserted within pneuoperitoneum.